1. Field of the Invention
The present invention relates to a bubbling evaporator for supplying vapor evaporated from a liquid together with a carrier gas by making the carrier gas blow into the liquid to cause bubbling, and particularly relates to prevention of backflow of the liquid to the exterior of a bubbling vessel and stabilization of the evaporated vapor pressure.
2. Description of the Prior Art
In a process for manufacturing semiconductor devices and the like by utilizing vapor deposition, a liquid organic metal or the like liquid is caused to bubble by carrier gas so as to be evaporated and the vapor thus evaporated is supplied for the deposition, together with the carrier gas.
FIG. 1 is a vertical sectional view showing a structure of such a conventional bubbling evaporator. An evaporator shown in FIG. 1 comprises a vessel 1 for containing liquid 2 of an organic metal such as trimethylgallium (TMG) and an inlet pipe 4 for causing the liquid to bubble by a carrier gas such as hydrogen (H.sub.2). In such an evaporator, the carrier gas blows through an inlet valve 3 and the inlet pipe 4 into the liquid 2 to cause bubbles. When these bubbles float up to the liquid surface, vapor evaporated from the liquid 2 is absorbed efficiently into the bubbles. The carrier gas including such evaporated vapor is supplied to a deposition station through an outlet valve 5.
However, if backpressure is applied in the vessel 1 of the above described evaporator, it might happen that the liquid 2 flows backward through the inlet pipe 4 to the valve 3 or any other arranged pipes outside the vessel 1 to remain there. Such liquid remaining outside the vessel 1 not only causes change of the evaporated vapor pressure but also involves danger at the time of removing the vessel 1 for maintenance since such liquid organic metal is generally inflammable. In addition, although the vessel 1 is generally disposed in a constant temperature bath for the purpose of controlling the evaporated vapor pressure, the temperature of the carrier gas is not stable enough and the temperature difference between the carrier gas and the liquid 2 is large since the carrier gas is sent directly into the liquid 2 through the pipe 4 from outside the vessel 1. Accordingly, the evaporated vapor pressure obtained is not sufficiently stable.